I don’t think knowing sorcery spells is an automatic apostasy offence in Heortling Society. Sure there are some people opposed to it but not everybody. The real offence would be concentrating on the sorcery spells and failing to pay proper respect to the Gods.

I think there are many Heortlings who use spells without even knowing that they are sorcery. But the Sages of Lhankor Mhy do know and they would usually refrain from using such blasphemous sources, because it corrupts the human soul to perform godless magic. Therefore Sages use the Alien Combination Machine to cleanse a grimoire of its corruption. Essentially they are making spells safe to use.

Peter and Robin, I don’t really disagree with either of you (well, maybe with Peter a little). But part of the reason I answered that way is that I’d say the concept of common magic is most straightforwardly handled in RQ3 by spirit magic and in RQ6 by folk magic. In both rule sets, taking sorcery skills is a relatively specialized undertaking that I think fits what you’re both describing fictionally.